<head>
  <title>Clear float</title>
  <style>
    .container {
      margin: 30px auto;
      width: 600px;
      height: 300px;

    }

    .wrapper {
      border: solid 3px #a33;
      /* overflow: hidden; */
      position: absolute;

    }

    .main {
      width: 100px;
      height: 100px;
      background-color: #060;
      margin: 10px;
      float: left;
    }
  </style>
</head>

<body>
  <div class="container">
    <div class="wrapper">
      <div class="main"></div>
      <div class="main"></div>
      <div class="main"></div>
    </div>
  </div>
</body>